EP3045551B2 - Motor vehicle component and body component - Google Patents

Description

The present invention relates to a method for manufacturing a motor vehicle component according to the features in claim 1.

From the DE 10 2005 054 847 B3 Hot-formed and press-hardened components are known which, after final forming and the adjustment of high-strength mechanical properties in the steel, undergo targeted heat treatment. Particularly in structural and/or safety components that are subjected to axial loads in the event of a crash, a component manufactured according to the aforementioned method should, on the one hand, be high-strength and, on the other hand, wrinkle in the event of a crash in order to dissipate energy in a controlled manner.

From the DE 197 43 802 A1 A method for hot forming and press hardening of a motor vehicle component is known, in which a heat post-treatment is subsequently carried out, wherein the component cools down slowly from the temperature of the heat post-treatment.

From the DE 10 2004 023 579 A1 A method for manufacturing a component from high-strength steel is known. This component can also be subjected to post-heat treatment and allowed to cool from this temperature.

According to current technology, heat treatment typically takes place in a temperature range between 320°C and 400°C and hardly alters the strength values established during the hot forming and press hardening processes. However, it simultaneously increases the material's ductility to such an extent that wrinkling is possible in the event of a crash.

Using methods known from the state of the art, it is possible to achieve a sufficiently precise adjustment of the desired material configuration for many series production processes.

The object of the present invention is therefore to demonstrate a hot-formed and press-hardened motor vehicle component which has a targeted material structure and is suitable for cost-effective mass production.

The present problem is solved by a method having the features in claim 1.

Further embodiments are part of the dependent claims. The motor vehicle component is manufactured, in particular as a body component and preferably as a structural component or safety component for a motor vehicle, by means of hot forming and press hardening, and is characterized in that joining flanges and/or coupling points and/or crash-relevant component areas are partially heat-treated in several steps.

The body component produced in this way has the particular advantage that it can deform in the desired manner in the event of an accident. This component-specific, defined deformation behavior can, for example, be achieved through wrinkling. Furthermore, the joining flanges and/or coupling points are more ductile due to the heat treatment according to the invention, so that in the event of an accident they tend to deform rather than tear.

Within the scope of the invention, a body component is understood to be an A-pillar, B-pillar, C-pillar, D-pillar, a bumper, a crash box, a front longitudinal member, a rear longitudinal member, a tunnel (for example, in the form of a transmission tunnel), a sill, a cross member, a seat cross member, a heel plate, a roof cross member, a floor panel, a side panel, a vehicle door, a tailgate, a hood, a roof area, or an instrument panel with various attachments. Other sheet metal components of a motor vehicle can also be considered body components.

A crash-relevant component area is, for example, a connection area of an A-, B-, or C-pillar, or a coupling area of a sill with a crossmember or longitudinal member. In general, crash-relevant component areas within the scope of the invention are those component areas that are subjected to particular stresses in a vehicle crash. These include, for example, connection areas characterized by the coupling of two components, or transition areas, such as the radii of a door opening in a vehicle body, or similar areas that are subject to high demands regarding deformation and durability in the event of a vehicle crash.

In a longitudinal beam that is heat-treated using the inventive method, areas can be created that deform in a controlled manner in the event of a vehicle crash. This deformation can, for example, take the form of folding or inward folding.

• Partielles Wärmebehandeln der Kraftfahrzeugkomponente in Bereichen, wobei die Bereiche zunächst auf eine Aufwärmtemperatur in einem Temperaturbereich zwischen 500 °C und 900 °C, bevorzugt zwischen 550 °C und 800 °C, insbesondere zwischen 700 °C und 800 °C aufgewärmt werden;
• Halten der Aufwärmtemperatur für eine Haltezeit;
• Abkühlen von der Aufwärmtemperatur in mindestens zwei Phasen.

The process for manufacturing the hot-formed and press-hardened motor vehicle component consisting of at least one hot-formed and press-hardened body component made of high-strength steel, which is used as a structural component and/or safety component for a motor vehicle, is carried out with the following process steps:

• Partial heat treatment of the motor vehicle component in areas, wherein the areas are first heated to a warming temperature in a temperature range between 500 °C and 900 °C, preferably between 550 °C and 800 °C, in particular between 700 °C and 800 °C;
• Maintaining the warm-up temperature for a holding period;
• Cooling from the heating temperature in at least two phases.

One advantage of the method according to the invention is that the desired material properties in the motor vehicle component can be achieved in a targeted and process-reliable manner. The component produced by hot forming and press hardening has a hard and brittle structure. Partial heat treatment using the inventive method below the austenitizing temperature transforms the material structure of the component in the heat-treated areas, resulting in a more ductile material structure. According to the invention, the heating process begins at a starting temperature that the component has after the press hardening process. This could, for example, be the ambient temperature. However, the starting temperature of the heating process is always lower than the martensite starting temperature (MS), preferably below 200°C.

The temperature range between 500°C and 900°C for heating or maintaining the heating temperature results in a particularly advantageous stress reduction in the specifically heat-treated areas, for example on joining flanges or on the edges of recesses that are subjected to a heat treatment according to the invention.

Using the example of a motor vehicle component used as a structural or safety component in a self-supporting body, the heat-treated area has a particularly beneficial effect on the crash performance of the body in the area where the motor vehicle component is used. For example, if an area in the form of a joining flange has been heat-treated using the method according to the invention, this joining flange is less prone to tearing, splitting, or cracking in the event of an accident and thus holds the surrounding structural or safety components together. This is particularly advantageous for occupant protection, especially when considering the passenger compartment. Within the scope of the invention, a joining flange is understood to be a flange area designed for connecting another component or component. This connection can be achieved by gluing, riveting, welding, brazing, or similar joining processes.

A further advantage arises in areas that are subject to intentional deformation in the event of an accident. This deformation is designed to dissipate energy into the vehicle body, thereby increasing crash safety for vehicle occupants. Another application is, for example, the targeted deformation of specific areas to enable particularly cost-effective accident repairs.

In the event of a crash, the areas heat-treated using the inventive method can be deformed in such a way that controlled folding and thus controlled energy absorption occurs. Furthermore, the heat-treated areas are less prone to cracking because their microstructure is more ductile compared to the hard and brittle microstructure of hot-formed and press-hardened materials.

The inventive method produces the desired material properties in a particularly reliable manner, suitable for large-scale production. Manufacturing variations in the form of manufacturing tolerances can thus be largely avoided, so that, for example, in the application of a car body designed by targeted CAD calculation with specific crash points, a high degree of manufacturing accuracy is ensured by using vehicle components produced with the inventive method.

In a preferred embodiment, the partial heat treatment is carried out on the joining flanges of the component. This offers the advantage that the joining flanges exhibit ductile material properties. In the case of a material-bonded connection by thermal joining, a microstructure transformation takes place in the heat-affected zone of the joining process. A ductile section of the component has a particularly beneficial effect on the welding process and the material structures that develop in the heat-affected zone after the welding process. These are also transformed into a ductile material structure by a partial heat treatment carried out using the method according to the invention. This, in turn, has a particularly beneficial effect on the durability of the welded seams in the event of a vehicle accident. Within the scope of the invention, "welds" refers to all welds produced by thermal joining. These can be, for example, continuous longitudinal welds, spot welds, or even interrupted welds.

In another preferred embodiment, partial heat treatment is performed on recesses in the component. These recesses may be present, for example, for weight optimization or to accommodate other components, such as a gearshift lever, a wiring harness, or similar items. Particularly in the area of the recesses and at their ends, cracks can form in the event of an accident, potentially extending across the entire component. By reducing the surface tension, a ductile material structure develops in this area. This structure resists cracking and thus also facilitates unintended deformation of the component.

Furthermore, stresses caused by alternating bending stresses, which are introduced into the bodywork, for example, by body torsion or other driving influences such as engine vibrations or similar, can be particularly favorably influenced by this method. Especially with regard to the longevity of a motor vehicle body, a particularly positive effect can be achieved by reducing the surface tension in the end region of cutouts through partial heat treatment using the method according to the invention.

The automotive component is constructed from at least two parts by coupling, and heat treatment is carried out at the coupling points. These at least two parts can be at least two hot-formed and press-hardened components. However, it can also be a single hot-formed and press-hardened component coupled to a second component manufactured using a conventional manufacturing or sheet metal fabrication process. A particular advantage here is that the hot-formed and press-hardened component is provided with the same positive effects of the invention as previously mentioned.

Furthermore, treating the coupling points with a method according to the invention also has a particularly beneficial effect on their load-bearing capacity and durability. In the area of coupling by thermal joining, a heat-affected zone is created in a weld seam, which in turn leads to a microstructural transformation. Depending on the coupling process used, for example, gas metal arc welding, laser welding, spot welding, seam welding, or similar processes, various material properties arise, some of which also entail undesirable side effects. For economic reasons related to large-scale production, however, the advantages of the respective welding process used outweigh the disadvantages. These disadvantages can, however, be eliminated cost-effectively and suitable for large-scale production using the method according to the invention.

The heat treatment of the welds has a particularly beneficial effect on their durability, corrosion resistance and deformation capacity.

Preferably, the heating is carried out over a period of up to 30 seconds, more preferably up to 20 seconds, particularly preferably up to 10 seconds, and especially up to 5 seconds. According to the inventive method, the heating can be carried out with a progressive, linear, or degressive temperature increase over time. A short heating phase to reach the heating temperature, in combination with a subsequent holding phase in which the heating temperature is maintained for a specified period, has a particularly advantageous effect on the process reliability of the partial heat treatment.

Preferably, the holding time is up to 30 seconds. More preferably, the holding time is up to 20 seconds, particularly preferably up to 10 seconds, and especially up to 5 seconds. By selectively controlling the material structure transformation at a constant temperature, influenced only by the duration of the holding time, the tempering process according to the invention can be carried out with particular process reliability. During the holding time, the achieved heating temperature is essentially maintained. A further temperature increase or decrease during the holding time is also conceivable within the scope of the invention. This temperature difference from the heating temperature is up to a maximum of 100 °C.

A further advantage resulting from the short heating and holding times is that heat transfer in the form of conduction is largely avoided. Furthermore, the inventive method can be particularly advantageously integrated into the cycle time of existing production processes with hot forming steps and subsequent manufacturing steps. The cycle times can be within a time window of 5 seconds to 30 seconds, preferably between 10 seconds and 15 seconds.

The heating and holding process steps can take place in a single fixture, which is also used for hot forming and press hardening the component. Alternatively, after hot forming and press hardening, the components can be transferred to a separate fixture for heating and temperature maintenance. This heating and temperature maintenance can be achieved, for example, through inductive heating or similar methods, which can be integrated into the production process depending on the application.

According to the present invention, cooling is carried out in at least two phases. Within the scope of the invention, the two cooling phases can be essentially the same length. It is particularly preferred that the first cooling phase be longer than the second. The cooling phases can again be carried out in a single device, in the heat treatment device, or in a separate cooling vessel. It is also conceivable within the scope of the invention to carry out the at least two different cooling phases in two separate cooling vessels.

The multi-phase cooling process of the heat treatment according to the invention makes it possible to achieve the desired microstructure transformation stage and thus the desired material properties in the partially heat-treated areas with particular process reliability, cost-efficiency, and high accuracy. Furthermore, the multi-phase cooling process allows it to be integrated into the ongoing production of a component in such a way that it can be individually adjusted to the cycle times of preceding and subsequent processing steps across a wide range, without negatively impacting the achievable microstructure transformations.

In a preferred embodiment, the second cooling phase takes place over a period of up to The cooling process is carried out for 120 seconds, preferably up to 60 seconds. In a further preferred embodiment, the first cooling phase cools the motor vehicle component to a temperature between 200 °C and 900 °C, preferably between 300 °C and 800 °C, and particularly between 500 °C and 700 °C.

In a second phase, the automotive component is cooled to a target temperature. Within the scope of the invention, this target temperature is below 200°C. Below a component temperature of 200°C, no further thermally induced component distortion occurs, which would negatively impact the production reliability of the process. However, it is also conceivable within the scope of the invention to carry out the cooling down to room temperature. The cooling profiles of the temperature difference, or the temperature profile over the cooling time, can again be progressive, linear, or degressive within the scope of the invention. A resulting advantage is that, after reaching the initial cooling temperature, essentially no further component distortion occurs.

In a further preferred embodiment of the method according to the invention, heating to the required temperature is achieved by means of induction and/or infrared heating. Within the scope of the invention, infrared heating refers, for example, to infrared emitters that enable lamp heating. An advantage arising from this in connection with the overall method is that very small local areas with a clearly defined boundary can be heat-treated. With the method according to the invention, the transition zone between the hot-formed and press-hardened unheat-treated area and the partially heat-treated area is preferably less than 100 millimeters, particularly preferably less than 50 millimeters, and especially between 1 and 20 millimeters. This allows for the targeted, local heat treatment of small, sharply defined areas.

Figur 1

zeigt verschiedene Temperaturverläufe der einzelnen Schritte der Wärmebehandlung über der Zeit;

Figur 2

eine perspektivische Ansicht einer A-Säule;

Figur 3

eine perspektivische Ansicht eines Rahmentunnels;

Figur 4

eine Kraftfahrzeugkomponente bestehend aus zwei miteinander gekoppelten Bauteilen;

Figur 5

ein Instrumententräger, bestehend aus mehreren Bauteilen und

Figur 6

einen Stoßfänger mit verschiedenen Anbauteilen.

Further advantages, features, and properties of the present invention will become apparent from the following description; preferred embodiments are illustrated with reference to the schematic drawings. These serve to facilitate understanding of the invention. They show:

Figure 1

shows different temperature profiles of the individual steps of the heat treatment over time;

Figure 2

a perspective view of an A-pillar;

Figure 3

a perspective view of a frame tunnel;

Figure 4

a motor vehicle component consisting of two interconnected components;

Figure 5

an instrument carrier consisting of several components and

Figure 6

a bumper with various attachments.

The same reference symbols are used in the figures for identical or similar parts, achieving corresponding or comparable advantages even if repeated description is omitted for the sake of simplicity.

Figure 1a Figure 1 shows a temperature profile over time with the time intervals according to the invention: warm-up time (t1), holding time (t2), cooling time first phase (t3) and cooling time second phase (t4). The warm-up temperature (T1) and a first cooling temperature (T2) are also shown on the temperature axis.

Starting with a hot-formed and press-hardened automotive component, which is essentially at a temperature below 200°C, it is heated to the warm-up temperature (T1) during the warm-up period. With an initial temperature below 200°C, but above room temperature, the residual heat energy from the hot-forming and press-hardening process is used for partial heat treatment according to the invention.

The heating process exhibits a linear temperature increase over time. After the heating period (t1) is complete, the heating temperature (T1) is maintained for a holding period (t2). The heating temperature (T1) is kept essentially constant throughout the entire holding period (t2). Temperature fluctuations in the form of a temperature increase or decrease are not shown here, but can occur during the holding period (t2) within the scope of the invention for reasons of desired material structure transformation or for cost reasons related to the production process.

After the holding time (t2) has elapsed, an initial cooling phase to a cooling temperature (T2) takes place. The temperature decreases linearly over the cooling time of the first phase (t3) to the cooling temperature (T2). The cooling temperature (T2) can be in a range between 100°C and a heating temperature (T1).

In a subsequent second cooling phase, a further linear temperature decrease occurs during the cooling time of the second phase (t4). This temperature decrease can essentially reach room temperature or a desired target temperature, which is not described in detail here. It is also conceivable within the scope of the invention that further cooling phases, which are not described in detail here, could take place.

Figure 1b shows an essentially similar temporal staggering of the heat treatment with the difference to Figure 1a that the temperature increase during the warm-up period (t1) has a progressive course and the cooling during the first and the The second phase has a progressively degressive temperature profile over time (t3, t4).

Figure 1 c shows in addition to Figures 1a and 1b , that the temperature profile during the warm-up period (t1) has a degressive profile and during the individual cooling phases has a progressive profile of the temperature decrease over time (t3, t4).

Within the scope of the invention, it is also conceivable to combine the temperature profile over time in mixed forms of progressive, linear and degressive profiles and also to realize a temperature change with a progressive, degressive or linear profile during the holding time (t2).

Figure 2 Figure 1 shows a motor vehicle component 1 in the form of an A-pillar 2 of a motor vehicle body (not shown in detail here). The A-pillar 2 has joining flanges 3 on its respective sides 2a, 2b, which are heat-treated using the method according to the invention. The A-pillar 2 therefore has high strength and hardness due to its central profile section 4, which guarantees the protection of a passenger compartment in the event of a crash. In its joining flanges 3, the material has a more ductile property compared to the central profile section, so that components connected to the joining flanges 3 (not shown in detail here) remain connected to the A-pillar 2 and no tearing occurs at the connection points, characterized by the joining flanges 3.

Figure 3 Figure 1 shows a motor vehicle component 1 in the form of a transmission tunnel 5, which is not a constructed motor vehicle component according to claim 1. The transmission tunnel 5 has a recess 6 and joining flanges 3 on both sides 5a, 5b and a central profile section 4. Here too, the end regions 7 of the recess 6 and the joining flanges 3 can be heat-treated using the method. In the event of a vehicle crash, the heat treatment of the end regions 7 of the recess 6 specifically prevents cracking, which would negatively affect the deformation behavior of the motor vehicle component 1, here in the form of the transmission tunnel 5.

Figure 4 Figure 1 shows a motor vehicle component 1 constructed from two coupled components 8 and 9. In the embodiment shown here, the upper component 8, referenced to the plane of the image, is a hot-formed and press-hardened component, and the lower component 9, also referenced to the plane of the image, is a component manufactured using conventional forming processes. The two components 8 and 9 are coupled to each other at coupling points 10. The coupling points 10 were heat-treated after the coupling process using a method according to the invention.

Figure 5 Figure 11 shows an instrument carrier 11, which is assembled from several individual components 12. The individual components 12 are coupled to each other via coupling points 10.

Figure 6 Figure 1 shows a bumper 13 with two crash boxes 14 and mounting plates 15 coupled to the crash boxes. The bumper 13 is coupled to the crash boxes 14 at coupling points 10 by thermal joining.

Reference symbol:

1 -

automotive component

2 -

A-pillar

2a -

Page 2

2b -

Page 2

3 -

joining flange

4 -

middle profile section

5 -

transmission tunnel

5a -

Page 5

5b -

Page 5

6 -

recess

7 -

End area

8 -

upper component

9 -

lower component

10 -

coupling point

11 -

Instrument carrier

12 -

individual component

13 -

Bumper

14 -

Crashbox

15 -

Mounting plate

t1 -

Warm-up time

t2 -

Holding time

t3 -

Cooling time first phase

t4 -

Cooling time second phase

T1 -

Warm-up temperature

T2 -

Cooling temperature first phase

Claims (9)

1. Method for producing a motor vehicle component (1) having at least one hot-formed and press-hardened body part (8, 9) made from high-strength steel, wherein the motor vehicle component (1) is used as a structural part and/or safety part for a motor vehicle, with the following method steps:

   - partially heat-treating the body part in zones, wherein the zones are first heated to a heat-up temperature (T1) in a temperature range between 500°C and 900°C, preferably between 550°C and 800°C, particularly between 700°C and 800°C;

   - maintaining the heat-up temperature (T1) for a holding time (t2);

   - cooling down from the heat-up temperature (T1) in at least two phases, wherein the motor vehicle component (1) is constructed from body parts (8, 9) by coupling and the heat treatment is carried out at the coupling sites (10).
2. The method according to claim 1, characterised in that the coupling is produced by thermal joining.
3. The method according to any one of claims 1 to 2, characterised in that the heating up is carried out over a period (t1) of up to 30 seconds, preferably up to 20 seconds, most preferably up to 10 seconds, particularly up to 5 seconds.
4. The method according to any one of claims 1 to 3, characterised in that the holding time (t2) is carried out over a period of up to 30 seconds, preferably up to 20 seconds, most preferably up to 10 seconds, particularly up to 5 seconds.
5. The method according to any one of claims 1 to 4, characterised in that the cooling time of the first phase (t3) is carried out for a longer duration in relation to the cooling time of the second phase (t4).
6. The method according to claim 5, characterised in that the second phase is carried out over a period (t4) of up to 120 seconds, preferably up to 60 seconds.
7. The method according to any one of claims 1 to 6, characterised in that the body part (8, 9) is cooled by the first phase of the cooling (t3) to a temperature (T2) of between 200°C and 900°C, preferably between 300°C and 800°C, particularly between 500°C and 700°C.
8. The method according to any one of claims 1 to 7, characterised in that the motor vehicle component is formed as an A-pillar, B-pillar, C-pillar, D-pillar, bumper, crash box, front longitudinal member, rear longitudinal member, tunnel, for example in the form of a transmission tunnel, sill, cross member, seat cross member, heel panel, roof cross member, floor panel, side panel, vehicle door, tailgate, engine bonnet, roof area or instrument panel support, wherein joining flanges and/or coupling sites and/or crash-relevant part zones are partially heat-treated in several steps.
9. The method according to any one of claims 1 to 8, characterised in that the motor vehicle component has a part-specific defined deformation behaviour due to crinkling, wherein joining flanges and/or crash-relevant part zones are partially heat-treated in several steps.